Self-locking screws reusable?

Chip Sylverne said:
It's not as simple as question as it appears. Some self-locking fasteners that lock by virtue of an angular or pitch change in the ramp of the threads are indeed re-usable many times. Fasteners that lock by virtue of patches, adhesives or inserts aren't. Fasteners that lock by virtue of lock washers such as internal or external star may be re- used, but the locking washers are one-time use. Nordlock being the exception, but as was pointed out, those too have their drawbacks.

The problem I had with Lycomings IPC is that it called these fasteners self-locking, but come to find out they aren't, they lock by virtue of a captive washer. As expensive as they are, I assumed they would lock by the threads and actually fall into the reusable category. Turns out that was wrong by a long shot. I'm a bit OCD when it comes to nomenclature, I guess.

Pursued this more out of curiosity than anything else. Glad I did, I learned a bunch.

BTW, think I found that oil leak we were chasing ;).
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That’s great you found the leak……I was being snarky. lol:) Merry Christmas
 
In other Lycomings, do they call out a separate bolt and washer? Has Lycoming been contacted and asked about this issue? Has an engine shop been asked how they deal with this kind of hardware?

It is a good question. I once discussed rusted and worn out hardware on a rental turbine engine. Of course the rental agency didn't want to do anything about it. I got them to email me their opinion on letterhead and with a signature from the tech rep. That hardware was worth thousands, but my signature and licence was going in the records.
 
You don’t have a Lycoming parts catalog? I posted the page from mine earlier in the thread.
 
I would think an STD-1204 1/4-20 bolt and lock & flat washers would be fine if there isn't some clearance of the head & washers problem.
 
Interesting. Same p/n, but in the O-540 IPC it's called self-locking, but in the IO-540 it's not. Mine's dated '91. Maybe Lyc's been down this road.
 
Chip Sylverne said:
Interesting. Same p/n, but in the O-540 IPC it's called self-locking, but in the IO-540 it's not. Mine's dated '91. Maybe Lyc's been down this road.
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Newest O320 IPC (Oct 2011) has a regular bolt, flat & lock washer. That's what I'd do.

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If I had a Lycoming with just the filter screen housing, I would toss the bolts and put in studs, same studs that are used at the intake ports or vacuum pump mounting. As long as there is room enough behind the screen to slide it off the studs, of course. Getting the housing, gasket and one bolt with washers all started is a bit of a pain. Much easier to put the gasket on over the studs, put the housing on, and put the washers and nuts on. Everything stays lined up.

The studs are double-ended, with the coarse thread that goes into the case or cylinder casting just a bit oversize so it jams in there. Double-nut the fine-thread end to put it in. They stay put unless the casting holes are really worn out, and if they are, they won't safely retain a bolt either.
 
Stewartb said:
I wouldn’t trust the threads in the case to hold the same self-locking screw twice. That’s a stupid system. Probably why it isn’t used these days.
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It also wears those holes a bit every time bolts of any sort are removed and reinstalled. Steel bolts and aluminum threads...the aluminum loses. The holes should be helicoiled.
 
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